I'm sure this has been asked before, mechanic precautions

Hey everyone,
My original post is here:
http://www.forabodiesonly.com/mopar/showthread.php?t=296681
I have found a mechanic to do the engine swap (slant6 to 360) on my 71 Dart. I'm wondering what things I should do to protect myself during this.

The deal is they're finding the 360/727, having it rebuilt, putting it in the car, exhaust/driveline etc. I've never had a mechanic do this amount of work to my car. Should I write a contract or something for both of us to sign, guarantee a warranty, etc?

I'm sure these types of questions have been asked before, but I didn't have any luck using the search function and finding it. I definitely don't want to get screwed over on someone that's going to cost a few grand.

Any advice is appreciated. Thanks!